1. Field of the Invention
The present invention relates to a method of developing a software system using Object Oriented Technology and frameworks.
2. Description of the Related Art
In order to maintain or enlarge their competitiveness, enterprises of almost every type of business all over the world have to rework and bring up to date their information technology to meet customer's requirements and thus to be successful in the market. But keeping an information system based on traditionally developed software up to date is at least an expensive undertaking, and in many cases it is an unsolvable problem. Object Oriented Technology or simply Object Technology, often abbreviated "OOT" or simply "OT", has the technical potential to overcome the problems associated with development, maintenance, and extension of software applications within a company's information system and to provide interoperability and adaptability across multiple applications and hardware platforms.
Object Oriented Technology describes a method for the development of operating software as well as application software for a computer system. Contrary to the traditional, non object oriented ways of developing software, Object Oriented Technology comprises and uses preengineered "methods" and "objects" for the development of software, comparable to tools and parts for the development of an automobile.
Similar to the development of an automobile, wherein not each required screw is developed individually, but standardized screws are used which can be individually adapted by shortening to the required length, within the development of software, Object Oriented Technology provides a "class" as a kind of software template from which individual "objects" can be instantiated. These classes are usually stored in a software library or a so called "class library". A class library is simply a collection of several classes stored together in a special filing format called a library.
In Object Oriented Technology an "object" is a self-contained piece of software consisting of related data and procedures. Data means information or space in a computer program where information can be stored, e.g. a name or an inventory part number. Procedures are parts of a program that cause the computer to actually do something, e.g. the parts of a program which perform calculations or the part of a program that stores something on a computer disk. In Object Oriented Technology, an object's procedures are called "methods".
The concept of an object being a self-contained piece of software having data and procedures inside itself is a new way of developing software. In non object oriented software, most of the data for an entire program is often grouped together near the beginning of the program, and the procedures then follow this common pool of data. This conventional method worked okay for smaller programs, but as soon as a piece of software started to grow and become somewhat complex, it become increasingly difficult to figure out which procedures were using which data. This made it quite difficult and expensive to debug or change traditional software programs.
In Object Oriented Technology it is generally easier to debug, maintain, and enhance object oriented software. The three most popular object oriented programming languages are probably "C++", "JAVA", and "Smalltalk". The concept that both data and methods are contained inside an object is called "encapsulation". Part of the concept of encapsulation is that an object has a predictable way of communicating with other objects, a so called predictable "interface" or sometimes also called the method contract.
Provided that interface will not be changed, the code or methods inside the object can be changed without disrupting other objects' ability to interact with that object. For example, a TAX CALCULATION object would have a predictable interface for use by PAYCHECK objects. Provided that interface will not be changed, the detailed program code inside the TAX CALCULATION object could be changed whenever the tax laws changed, and no other objects in the payroll system would have to know anything about such changes.
In Object Oriented Technology the term "inheritance" is used to communicate the concept that one object can inherit part of its behavior and data from another object, e.g. since an employee is a type of person, an EMPLOYEE object might inherit the characteristics of a PERSON object, such as having name, birth date, and address data, as well as an EMPLOYEE object might inherit methods for updating and displaying these data.
Even if an object inherits some of its characteristics from other objects, that object can, and usually would, also have its own non-inherited characteristics, e.g. whereas a PERSON object would have an inheritable method to display a person's address, a PERSON object would probably not have a method for displaying paycheck history, since not all persons get paychecks. Because an EMPLOYEE object could not inherit this method from a PERSON object, an EMPLOYEE object would have to define its own method for displaying paycheck history.
Although Object Oriented Technology clearly seems to be the most sophisticated way for the development, maintenance, and extension of software applications, many companies developing software applications are concerned about the cost and risks involved with the rework of existing applications and with the construction of new applications using Object Oriented Technology. For those software application developers, a technical foundation for software applications has to be built as a tool using Object Oriented Technology as the basis, allowing each developer to develop highly unique software products. This technical foundation is formed by frameworks comprising the basic application structure which software application developers previously had to develop by themselves.
In Object Oriented Technology the term "framework" is used to describe a reusable set or collection of classes which work together to provide a commonly needed piece of functionality not provided by any of the individual classes inside the framework. Thus a framework defines a specific way in which multiple objects can be used together to perform one or more tasks which no single object performs. In other words, a framework is a reusable, predefined and preengineered bundle of several objects which address a recurring programming problem.
Frameworks provide a way of capturing a reusable relationship between objects, so that those objects do not have to be reassembled in that same relationship every time they are needed. Frameworks provide a way of grouping multiple objects together to perform some function which should not have to be thought through each time at the underlying object level. For example, a PRINT framework would consist of all the objects necessary for a programmer to easily print something on any printer, and would probably include objects for printer selection, spooling to disk or error detection as "out of paper". Frameworks can be regarded as an group of software objects which contain a technical foundation for a software application. For example in the business field of Financial, Logistic and Distribution or Production. Although a framework represents a skeleton of a software application, usually a framework is not an executable software program.
By providing frameworks as the technical foundation for developing software applications, the following problems have to be addressed:
Applications have to support all hardware platforms and related software operating systems relevant on the market. Applications have to fulfill the requirements related to client/server configurations including the requirement for graphical user interfaces and windowing techniques. Also, applications have to offer internet compatibility and access on demand. Furthermore applications have to provide integrated solutions with respect to installed software.
In particular, as an object within a framework progresses through processing and states there arises the requirement to modify the object, to modify existing abilities of the object or to provide new abilities for the object. For example, as a sales order is processed, its responsibilities change, e.g. only after a sales order is confirmed, it can be printed. A print method could be provided on the sales order, however its contract would be very weak.
As objects change their behavior while they are used in a dynamic and flexible manner, the changes have to be added, removed or suspended temporarily. This requirement can be solved by using a composite object which delegates the behavioral requests via a chain of responsibility across the objects making up the composite. However, traversal of the objects is very inefficient, especially when the objects making up the composite are in a client/server environment and must be transported on each usage, or when a behavior is not supported (all objects in the composite have to be visited), or because a list of all supported behavior is needed.
In addition, JAVA objects do not change behavior dynamically but still follow the chain of responsibility concept for method invocation.
For the creation of objects, an abstract factory can be used, see e.g. E. GAMMA et al: "Design Patterns: elements of reusable object-oriented software", Addison-Wesley, 1995, ISBN 0-201-63361-2. This use of an abstract factory causes the developer creating objects, in particular in a JAVA-based client/server environment, to have to deal with significant complexities, including
managing "type safety", including being aware of the JAVA interface and implementation class that together make up the implementation of a business object class in a JAVA based client/server environment, PA1 guaranteeing uniqueness of object identity, PA1 ensuring proper object ownership, PA1 and determining the location of a persistent object.
Within the accompanying figures, representation standards for classes, objects, relationships etc. are used at least partly according to Grady Booch: "Object-Oriented Analysis and Design with Applications", second edition, The Benjamin/Cummings Publishing Company, Inc., Redwood City, Calif., USA.